This invention relates to a method of rolling metal materials to round cross-sectional shape, and more particularly to improvements of the rolling method with respect to the accuracy of dimensional control for finish gauge.
In the rolling of metals such as steel to a round cross-sectional shape, attempts have been made to increase the accuracy of dimensional control for finish gauge by removing tension from the work being rolled in such a manner, as, for example, to permit formation of a loop between successive two roll stands, or, upon detection of the tension to automatically control the peripheral speed of the work roll. These methods are, however, because they fundamentally suffer from the limitation of the response speed and reliability of automatic control and are not suitable for use in achieving additional improvement of the accuracy of dimensional control over the heretofore attained level of about +0.2 to about +0.4 mm, depending upon the sizes of rolled products. Also, there are disadvantages of increasing the cost of equipment necessary to perform them, and of requiring additional spare wide floor space on which the equipment is to be installed. Further, significant numbers of rolling situations are encountered where secondary working operations will be found necessary as the heretofore attained level of dimensional control is not sufficiently high. For example, a considerable percentage of metal bars and wires after having been finish rolled must be further subjected to drawing or likewise forming applications.
Where a small reduction is desired, it is impossible to use the conventional rolling method adapted to produce a round cross-sectional shape, because this method must be operated with a large reduction which in turn calls for a large increase in the diameter of the work roll with the corresponding increase in the distance between the successive grooves. This leads to a high probability of the occurrence of twist in the work being rolled so that the percentage of rolled products which will be found acceptable with respect to the finish dimensions is decreased.
On the other hand, Morgan block mills are known which are representative of the various types of block mills used in the intermediate and/or finish rolling of steel material, but their primary aim is to achieve the speed-up of production run and the compactness of the mill equipment itself with the help of employing a relatively axial ratio of the oval groove, so that the reduction can not be limited to small orders. Thus, the deviation of the actual values of the dimensions of the finished products from the specific and ideal ones is of the order of .+-.0.2 mm. In addition thereto, it is recognized that it is necessary to provide an entrance roller guide positioned in front of a finishing groove for the purpose of preventing impartment of twist to the work being rolled.